The present invention pertains to a projection television receiver having an improved lens system whereby the size of the television receiver can be reduced.
FIG. 1 depicts a conventional lens system A for use in a projection television receiver. In this system, three lenses 1, 2 and 3 are employed with a reflector 4 positioned between the lenses 2 and 3 so as to deflect the optical axis by substantially 90.degree.. The lens system A of FIG. 1 is more compact than the lens system B of FIG. 2 which employs no such reflector 4.
FIGS. 3 and 4 show schematic cross-sectional views of projection television receivers employing a lens system of the type shown in FIG. 1. In the receiver of FIG. 3, the reflector 4 in the lens system A is inclined slightly with respect to the plane of the base of the cabinet 5. An image formed on the face of a projection-type cathode-ray tube 6 is enlarged by the lens system A, and then reflected by mirrors 7 and 8 onto a projection screen 9 at the front of the cabinet 5. In the projection television receiver shown in FIG. 4, the reflector 4 of the lens system A is oriented at an angle of about 45.degree. with respect to the plane of the base of the cabinet 5. In this case, the longitudinal axis of the cathode-ray tube 6 can be made more nearly perpendicular to the plane of the base of the cabinet 5, thereby reducing the depth of the cabinet 5. In this case, a mirror 10 arranged adjacent the top of the cabinet 5 is required to deflect the optical axis of the projected beam against the mirror 8, from which it is reflected towards the screen 11.
Although the lens system A shown in FIG. 1 is advantageous in that the depth of the cabinet can be reduced, nevertheless, disadvantages are involved in that the optical path from the lens to the screen is relatively long. This necessitates the use of a lens having a long focal length, and accordingly, a small F-number. Hence, in order to maintain a sufficiently bright image on the screen, it is necessary to employ a lens of large size.